It is common practice to provide a two-speed power-take-off (PTO) drive shaft for a tractor whereby different associated implements can be selectively driven at the two different shaft speeds. In accomplishing this, there has been proposed the employment of two different PTO shafts which alternately mount on the tractor gear box or the like, as well as the employment of a single shaft which mounts on the gear box in two different locations.
In accordance with the teachings of U.S. Pat. No. 3,352,165, assigned to the same assignee as the present invention, a PTO shaft is releasably disposed in a driving sleeve so that the shaft is driven by a splined connection with the sleeve, and can be reversed end-for-end in the sleeve. A two-position clutch element is operatively disposed between the driving sleeve and two associated driving gears, which two gears are rotatable at different speeds.
The clutch element is shiftable between the two driving gears for rotating the sleeve at two different speeds, typically 540 rpm and 1000 rpm. The PTO shaft is longer on one end, from its generally centrally located splines, than it is on its other end. When the shorter end of the shaft is inserted into the driving sleeve, the shaft splines interengage the sleeve splines, but the shaft does not act to shift the clutch element axially. The clutch element thus drives the sleeve (and shaft) at the first of two speeds.
In order to select the other speed, the longer end of the shaft is inserted into the sleeve and engages an inner sleeve connected to the shiftable clutch element, thus effecting axial movement of the clutch element as the shaft splines are engaged with the sleeve splines. The clutch element acts to couple the driving sleeve with the second one of the associated driving gears, whereby the sleeve and shaft are driven at the second PTO speed.
The opposite end portions of the PTO shaft are typically formed with splines each having a different number of teeth. The end portions of the PTO shaft project outwardly from the gear box, which permits the operator to visually determine what speed the shaft will rotate by leaving the cab and observing the difference in the number of spline teeth in the projecting end portion.
In recent years there has been concern raised by the American Society of Agricultural Engineers (ASAE) and the Society of Automative Engineers (SAE) regarding the lack of an indicator of the speed of the PTO shaft located in the tractor cab for convenient reference by the tractor operator. This concern is in part based on the fact that it is possible to "overspeed" the PTO shaft on some tractors, which can cause accessory equipment damage or failure. Additionally, efficient operation of the equipment is promoted by providing the operator with an arrangement of ascertaining PTO shaft speed without requiring visual observation of the shaft.